The present invention relates to a seat belt retractor.
DE 196 40 842 A1 teaches a seat belt retractor that comprises a belt reel mounted rotatably on a frame for retracting and uncoiling the seat belt, a blocking device for blocking the rotation of the belt reel, a control element for actuating the blocking device and a belt webbing and/or vehicle-sensitive sensor arrangement which activates actuation of the blocking device via the control element. The known seat belt retractor also comprises a load limiter which allows a load-limiting rotation of the belt reel relative to at least one part of the load limiter held by the blocking device when the blocking device is actuated.
The present invention ensures that, after operation of the load limiter, for example as a result of a crash, the blocking device is guided into a maintained blocking position or into readiness for a permanent blocking position. This is achieved in that the load-limiting rotation of the belt reel brings about this maintained blocking position or readiness for the blocking position of the blocking device. The readiness for continuous blocking of the belt reel can be achieved, in particular, by a permanently maintained pre-blocking state in which the control element is rotationally engaged with the belt reel. As a result of the continuous blocking of the belt reel, the seat belt retractor no longer has a winding function, at least in the belt extraction direction. This makes it clear to the user that load limitation has been implemented. The seat belt can optionally still be used as a xe2x80x9cstatic beltxe2x80x9d, possibly for a workshop run. Blocking of the belt reel is maintained at least until the seat belt is released, removed and optionally wound in the direction of the parked position owing to the restoring force of the motive spring acting on the belt reel.
Advantageously, the blocking device can be moved into the permanent blocking position after a defined rotational angle of the load-limiting rotation of the belt reel. As a result, the windability of the belt reel is put out of operation only beyond a defined threshold or crash severity. The winding capacity of the belt reel is maintained in the event of a minor crash.
To maintain this permanent blocking position or readiness, the control element with which the blocking device is actuated can be held by a holding device which is actuated during the load-limiting rotation, in the position where the blocking device is brought into the blocking position by a short-stroke concomitant rotation in the belt extraction direction. The sensor arrangement which causes the control element to move into this position is fixed in a pre-blocking position by the holding device. Preferably, the belt webbing-sensitive part of the sensor arrangement is fixed in the pre-blocking position for this purpose. Relatively slight forces are sufficient to bring the holding device, by the load-limiting rotation of the belt reel, into the position in which the sensor arrangement and, in particular, the belt webbing-sensitive part of the sensor arrangement is fixed in the pre-blocking position. The belt webbing-sensitive mass of the sensor arrangement can thus be held in a position which brings about the blocking position of the blocking device.
The invention can be used in seat belt retractors with load limiters in which the load limiter produces the necessary load limitation or decelerating effect on extraction of the belt webbing during the load-limiting rotation of the belt reel owing to the consumption of energy, for example owing to deformation work as in a torsion bar or friction as in load limiters formed from plates or friction linings.